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#include <sys/types.h>#include <netinet/in.h>
Sockets bound to the Internet protocol family use the following addressing structure:
struct sockaddr_in { short sin_family; u_short sin_port; struct in_addr sin_addr; char sin_zero[8]; };When using sockets, the
sin_family
field is
specified in host order, and the sin_port
and
sin_addr
fields are specified in network order.
Sockets may be created with the local address INADDR_ANY to affect ``wildcard'' matching on incoming messages. The address in a connect(SSC) or sendto (see send(SSC)) call may be given as INADDR_ANY to mean this ``host''. The distinguished address INADDR_BROADCAST is allowed as a shorthand for the broadcast address on the primary network if the first network configured supports broadcast.
When using the Transport Layer Interface (TLI),
transport providers such as
tcp(ADMP)
support addresses whose length varies from eight to sixteen
bytes. The eight byte form is the same as a
sockaddr_in
without the sin_zero
field. The sixteen byte form is identical to
sockaddr_in
. Additionally, when using
TLI, the sin_family
field is accepted
in either host or network order. For communicating with
other implementations via RFS, the preferred form
is eight bytes with sin_family
in network order.
The 32-bit Internet address contains both network and host parts. It is frequency-encoded; the most-significant bit is clear in Class A addresses, in which the high-order 8 bits are the network number. Class B addresses use the high-order 16 bits as the network field, and Class C addresses have a 24-bit network part. Sites with a cluster of local networks and a connection to the Internet may chose to use a single network number for the cluster; this is done by using subnet addressing. The local (host) portion of the address is further subdivided into subnet and host parts. Within a subnet, each subnet appears to be an individual network; externally, the entire cluster appears to be a single, uniform network requiring only a single routing entry. Subnet addressing is enabled and examined by the following ioctl(S) commands on a datagram socket in the Internet ``communications domain''; they have the same form as the SIOCIFADDR command (see Intro(ADMP)).